What is sapovirus?

Sapovirus: A Significant Cause of Viral Gastroenteritis

Sapovirus is a member of the Caliciviridae family that causes acute gastroenteritis in humans of all ages, characterized by diarrhea, vomiting, and abdominal pain, with symptoms typically lasting 1-4 days. 1, 2

Characteristics and Classification

• Sapoviruses belong to the genus Sapovirus within the family Caliciviridae, which also includes noroviruses (Norwalk-like viruses) 1, 2
• They are nonenveloped, single-stranded RNA viruses with high genetic and antigenic diversity 2
• Sapoviruses are classified into multiple genogroups (GI, GII, GIV, and GV) with at least 14 different genotypes identified in humans 3
• The virus was first discovered in 1976 through electron microscopy of diarrheal samples 2
• The name "Sapovirus" comes from Sapporo, Japan, where an outbreak occurred, similar to how other Norwalk-like viruses are named after outbreak locations 1

Clinical Presentation

• Incubation period is 1-3 days, with illness typically lasting 4 days 1
• Common symptoms include:
  • Vomiting and diarrhea (diarrhea is more common than vomiting in many cases) 4
  • Upper respiratory symptoms and fever may occur less frequently 1
  • Abdominal cramps, headache, and myalgia can also be present 4
• While generally self-limiting, sapovirus can cause:
  • Persistent diarrhea in immunocompromised patients 5
  • Rarely, severe cases leading to septic shock have been reported 6

Epidemiology

• Sapovirus affects people of all ages, though historically it was thought to primarily affect children 1, 4
• By age 2 years, studies show 82% of children in endemic areas have had at least one sapovirus infection 3
• Attack rates in outbreaks range from 50% to 70% 1
• Most people acquire antibodies by age 12, with peak acquisition between 3 months and 6 years 1
• Immunity appears to be genotype-specific, allowing for multiple infections by different genotypes 3
• Young adults may retain effective immunity from earlier exposures, but immunity may wane with age, making the elderly susceptible again 1

Transmission

• Primary transmission routes include:
  • Person-to-person contact (most common for endemic disease) 1
  • Contaminated food, particularly shellfish 1
  • Contaminated water 1
  • Cold foods 1
• Outbreaks commonly occur in institutional settings such as:
  • Schools 1
  • Nursing homes 1
  • Hospitals (nosocomial outbreaks) 4
  • Infant-mother hospital units 1

Diagnosis

• Reverse transcription-PCR (RT-PCR) is the most widely used method for detection due to:
  • High sensitivity and specificity 2
  • Ability to detect the broad range of sapovirus genotypes 2
• Electron microscopy can identify the characteristic calicivirus morphology but is less sensitive 2
• Commercial antigen detection kits specifically for sapovirus are not widely available, unlike those for rotavirus 1

Treatment and Prevention

• Treatment is primarily supportive care focused on:
  • Maintaining hydration and electrolyte balance 6
  • Managing symptoms 5
• For immunocompromised patients with persistent infection:
  • Reduction of immunosuppressant therapy may help improve symptoms 5
  • Nitazoxanide has shown some effectiveness in reducing symptom duration in limited cases 5
• Prevention strategies include:
  • Good hand hygiene with soap and water for at least 20 seconds 1
  • Proper disinfection of contaminated surfaces with chlorine bleach solution 1
  • Exclusion of ill food handlers and healthcare workers until 48-72 hours after symptom resolution 1
  • Isolation of ill residents in institutional settings for 24-48 hours after symptom resolution 1

Public Health Implications

• Sapovirus is increasingly recognized as an important cause of gastroenteritis outbreaks, especially as diagnostic capabilities improve 2
• The virus has been associated with both sporadic cases and outbreaks globally 2
• Multiple genotypes circulate simultaneously, complicating immunity and potential vaccine development 3
• Chronic infections and long-term viral shedding can occur in immunocompromised individuals, presenting management challenges 5